Chapter 3: EMPIRE and After - NASA 3.pdf · They assumed a Nova rocket capable of lifting 250 tons to Earth orbit. For comparison, the largest planned Saturn rocket, the Saturn C-5

Manned exploration of Mars is the key mis-sion in interplanetary space flight. Man mustplay a key role in the exploration of Marsbecause the planet is relatively complex,remote, and less amenable to exploration byunmanned probes than is the [M]oon . . . seri-ous interest in the Manned Mars Mission isspringing up . . . with many planning studiesbeing performed by several study teamswithin [NASA] and within industry . . . .Perhaps the most important result emergingfrom the present studies is the indicationthat the Manned Mars Mission can be per-formed in the relatively near future withequipment and techniques that will for themost part be brought into operation by theApollo Project . . . the Manned Mars Missionis rapidly taking shape as the direct follow-on to the Apollo Project. (Robert Sohn, 1964)1

EMPIRE

Ernst Stuhlinger’s Research Projects Division was thesmaller of two advanced planning groups in ABMA.The larger, under Heinz Koelle, became the MarshallSpace Flight Center’s Future Projects Office. Until1962, Koelle’s group focused primarily on lunar pro-grams—Koelle was, for example, principal author ofthe U.S. Army’s 1959 Project Horizon study, whichplanned a lunar fort by 1967. Koelle’s deputy, HarryRuppe, also supervised a limited number of Mars stud-ies. Ruppe had come from Germany to join the vonBraun team in Huntsville in 1957.

In the 1962-1963 period, however, the Future ProjectsOffice spearheaded NASA’s Mars planning efforts. Asdiscussed in the last chapter, Marshall’s primary focuswas on launch vehicles. Advanced planning becameimportant at Marshall in part because of the long leadtimes associated with developing new rockets.Marshall director von Braun foresaw a time in the mid-1960s when his center might become idle if no goalsrequiring large boosters were defined for the 1970s. AsT. A. Heppenheimer wrote in his 1999 book The SpaceShuttle Decision,

The development of the Saturn V set the pacefor the entire Apollo program. This Moonrocket, however, would have to reach anadvanced state of reliability before it could be

used to carry astronauts. The Marshall staffalso was responsible for development of thesmaller Saturn IB that could put a pilotedApollo spacecraft through its paces in Earthorbit. Because both rockets would have tolargely complete their development beforeApollo could hit its stride, von Braun knewthat his [C]enter would pass its peak of activ-ity and would shrink in size at a relativelyearly date. He would face large layoffs evenwhile other NASA [C]enters would still beactively preparing for the first mission to theMoon.2

Mars was an obvious target for Marshall’s advancedplanning. Von Braun was predisposed toward Marsexploration, and landing astronauts on Mars providedample scope for his Center to build new large boosters.The timing, however, was not good. The Moon would, ifall went well, be reached by 1970—but NASA wouldcertainly not be ready to land astronauts on Mars sosoon. For one thing, planners needed more data on theMartian environment before they could design landers,space suits, and other surface systems. What Marshallneeded was some kind of short-term interim programthat answered questions about Mars while still provid-ing scope for new rocket development.

A 1956 paper by Italian astronomer Gaetano Crocco,presented at the Seventh International AstronauticalFederation Congress in Rome, offered a possible wayout of Marshall’s dilemma.3 Crocco demonstratedthat a spacecraft could, in theory, fly from Earth toMars, perform a reconnaissance Mars flyby, andreturn to Earth. The spacecraft would fire its rocketonly to leave Earth—it would coast for the remainderof the flight. The Mars flyby mission would requireless than half as much energy—hence propellant—asa minimum-energy Mars stopover (orbital or landing)expedition. This meant a correspondingly reducedspacecraft weight. Total trip time for a Crocco-typeMars flyby was about one year; for the type of missionvon Braun employed in The Mars Project (1953), triptime was about three years.

Flyby astronauts would be like tourists on a tour bus,seeing the sights from a distance in passing but not get-ting off. Crocco wrote that they would use “a telescopeof moderate aperture . . . to reveal and distinguish nat-ural [features] of the planet . . . .” He found, however,that Mars’ gravity would deflect the flyby spacecraft’s

11Humans to Mars: Fifty Years of Mission Planning, 1950–2000

Chapter 3: EMPIRE and After

course so it missed Earth on the return leg if it flewcloser to Mars than about 800,000 miles. Such a distantflyby would, of course, “frustrate the exploration scopeof the trip.”

To permit a close flyby without using propellant, Croccoproposed that the close Mars flyby be followed by aVenus flyby to bend the craft’s course toward Earth.The Venus flyby would be an exploration bonus, Croccowrote, allowing the crew to glimpse “the riddle which isconcealed by her thick atmosphere.” Crocco calculatedthat an opportunity to begin an Earth-Mars-Venus-Earth flight would occur in June 1971.4

From a vantage point at the start of the twenty-firstcentury, a piloted planetary flyby seems a strangenotion, yet in the 1960s NASA gave nearly as muchattention to piloted Mars flybys as it did to pilotedMars landings. Piloted Mars flybys are now viewedfrom the perspective of more than three decades of suc-cessful automated flyby missions (as well as orbitersand landers). Of the nine planets in the solar system,only Pluto has not been subjected to flyby examinationby machines. Robots can do flybys, so why entail theexpense and risk to crew of piloted flybys?

Indeed, there were critics at the time the FutureProjects Office launched its Early Manned Planetary-Interplanetary Roundtrip Expeditions (EMPIRE) pilot-ed flyby/orbiter study. For example, Maxime Faget,principal designer of the Mercury capsule, coauthoredan article in February 1963 which pointed out that apiloted Mars flyby would “demand the least [propul-sive] energy . . . but will also have the least scientificvalue” because of the short period spent near Mars. Headded that data on Mars gathered through a pilotedflyby would be “in many ways no better than thosewhich might be obtained with a properly operating,rather sophisticated unmanned probe.”5

The key phrase in Faget’s criticism is, of course, “prop-erly operating.” When the Future Projects Officelaunched EMPIRE in May-June 1962, robot probes didnot yet possess a respectable performance record. TheMariner 2 probe carried out the first successful flybyexploration of another planet (Venus) in December1962, midway through the EMPIRE study, but theother major U.S. automated effort, the Ranger lunarprogram, was off to a shaky start. That series did notenjoy its first success until Ranger 7 in July 1964. Thefirst successful Mars flyby did not occur until a year

after that. In fact, one of the early justifications forpiloted flybys was that the astronauts could act as care-takers for a cargo of automated probes to keep themhealthy until just before they had to be released at thetarget planet.

Faget also believed that the “overall planning of a totalspaceflight program should be based on a logical seriesof steps.” Mercury and Gemini would provide basic expe-rience in living and working in space, paving the way forApollo, which would, Faget explained, “have the first realmission.” After that, NASA should build an Earth-orbit-ing space station and possibly a lunar base.6

For Faget, a piloted Mars flyby mission in the 1970swas a deviation from the model von Braun popularizedin the 1950s, which placed the first Mars expedition acentury or more in the future. Faget avoided mention-ing, however, that he had already been compelled torationalize Kennedy’s politically motivated drive forthe Moon. Going by von Braun’s logical blueprint, pilot-ed lunar flight should have been postponed until afterthe Earth-orbiting space station was in place.

For the EMPIRE study, three contractors studied pilot-ed flyby and “capture” (orbiter) expeditions to Mars andVenus. Aeronutronic studied flybys7; Lockheed looked atflybys and, briefly, orbiters8; and General Dynamicsfocused on orbiter missions.9 Aeronutronic’s studysummed up EMPIRE’s three goals:

• Establish a requirement for the Nova rocketdevelopment program.

• Provide inputs to the joint AEC-NASA nuclear rocket program, which had been established in1960 and included a flight test program over which Marshall had technical direction.

• Explore advanced operational concepts neces-sary for flyby and orbiter missions.10

The first two goals were contradictory as far as spacecraftweight minimization was concerned. Seeking justifica-tion for a new large rocket provided little incentive forweight minimization, while one of the great attractions ofnuclear-thermal rockets was their increased efficiencyover chemical rockets, which helped minimize weight.The contractors’ tendency not to tightly control spacecraftweight assisted them with crew risk minimization. Forexample, all three contractors saw fit to include in their

12 Monographs in Aerospace History


EMPIRE designs heavy spacecraft structures for gener-ating artificial gravity.

Lockheed identified two main Mars flyby trajectoryclasses, which it nicknamed “hot” and “cool.” In the for-mer, the piloted flyby spacecraft would drop insideEarth’s orbit (in some launch windows Venus flybyoccurred), reach its farthest point from the Sun (aphe-lion) as it flew by Mars, and return to Earth about 18months after launch. In the latter, the flyby spacecraftwould fly out from Earth’s orbit, pass Mars about 3months after launch, reach aphelion in the AsteroidBelt beyond Mars, and return to Earth about 22months after launch.

The Aeronutronic team opted for a “hot” trajectory.They assumed a Nova rocket capable of lifting 250 tonsto Earth orbit. For comparison, the largest plannedSaturn rocket, the Saturn C-5 (as the Saturn V wasknown at this time) was expected to launch around 100tons. One Nova rocket would thus be able to launch theentire 187.5-ton Aeronutronic flyby spacecraft intoEarth orbit.

Aeronutronic’s “design point mission” had the flybyspacecraft leaving Earth orbit between 19 July 1970and 16 August 1970, using a two-stage nuclear-thermalpropulsion system. Aeronutronic’s design retained theempty second-stage hydrogen propellant tanks to helpshield the command center in the ship’s core againstradiation and meteoroids. Two cylindrical crew com-partments would deploy from the core on booms; thenthe ship would rotate to provide artificial gravity. AnAEC-developed radioisotope power source woulddeploy on a boom behind the ship. At the end of theflight the crew would board a lifting body Earth-returnvehicle and separate from the ship. A two-stage retro-rocket package would slow the lifting body to a safeEarth atmosphere reentry speed while the abandonedflyby ship sailed by Earth into orbit around the Sun.

Lockheed also emphasized a rotating design for itsEMPIRE spacecraft. In the company’s report, the flybycrew rode into orbit on a Saturn C-5 in an ApolloCommand and Service Module (CSM) perched atop afolded, lightweight flyby spacecraft. A nuclear upperstage would put the CSM and flyby ship on course forMars. The CSM would then separate and the flybyspacecraft would automatically unfold two long boomsfrom either side of a hub. The CSM would dock at the

end of one boom to act as counterweight for a cylindricalhabitation module at the end of the other boom. Whenthe ship rotated, the CSM and habitation module wouldexperience acceleration the crew would feel as gravity.

The weightless hub at the center of rotation would con-tain chemical rockets for course correction propulsion,a radiation shelter, automated probes, and a dish-shaped solar power system. At Mars, the crew wouldstop the spacecraft’s rotation and release the probes. Atjourney’s end, the crew would separate from the flybycraft in the CSM, fire its rocket engine to slow down,discard its cylindrical Service Module (SM), and re-enter Earth’s atmosphere in the conical CommandModule (CM). The abandoned flyby craft would fly pastEarth into solar orbit. Lockheed’s report mentionedbriefly how a Mars orbiter mission might investigatethe Martian moons Phobos and Deimos.11

The General Dynamics report was by far the mostvoluminous and detailed of the three EMPIRE entries,reflecting a real passion for Mars exploration on thepart of Krafft Ehricke, its principal author. Ehrickecommanded tanks in Hitler’s attack on Moscow beforejoining von Braun’s rocket team at Peenemünde. Hecame to the U.S. in 1945 with the rest of the von Braunteam but left in 1953 to take a job at General Dynamicsin San Diego, California. There he was instrumental inAtlas missile and Centaur upper-stage development. Inthe late 1950s he became involved in GeneralDynamics advanced planning.

Ehricke’s team looked at piloted Mars orbiter missions.These would permit long-term study of the planet fromclose at hand, thus answering critics who complainedthat piloted flybys would spend too little time nearMars. General Dynamics’ 450-day Mars orbiter missionwas set to launch in March 1975.

Modularized Mars ships would travel in “convoys”made up of at least one crew ship and two automatedservice ships. Ship systems would be “standardized asmuch as practical” so that the crew ship could can-nibalize the service ships for replacement parts. If ameteoroid perforated a propellant tank, for example,the crew would be able to replace it with an identicaltank from a service ship. The ships would carry small“tugboat” spacecraft for moving propellant tanks andother bulky spares.12 This approach—providing many



spares—helped minimize risk to crew, but would dra-matically boost overall expedition weight.

General Dynamics described many possible ship con-figurations; what follows was typical. The companyallotted a nuclear propulsion stage for each majormaneuver. After performing its assigned maneuver, thestage would be cast off. Ehricke’s team estimated thatnuclear engine flight testing would have to occurbetween May 1968 and April 1970 to support a March1975 expedition. The M-1 engine system would performManeuver-1 of the Mars expedition, escape from Earthorbit (hence its designation). The M-2 engine systemwould slow the ship so Mars’ gravity could capture itinto Mars orbit, and M-3 would launch the spacecraftout of Mars orbit toward Earth. The M-4 engine systemwould slow the ship at Earth at the expedition’s end.

Attached to the front of the M-4 stage would be the 10-foot-diameter, 75-foot-long spine module, or “neck,”which served two functions: in addition to separatingthe astronauts from the nuclear engines to minimizecrew radiation exposure, it would place distancebetween the crew and the ship’s center of gravity, mak-ing the artificial gravity spin radius longer.

General Dynamics opted arbitrarily for providing arti-ficial gravity equal to 25 percent of Earth’s surfacegravity and estimated that five rotations per minutewas the upper limit for crew comfort. As engine sys-tems were cast off, however, the ship’s center of rotationwould shift forward. For example, before the M-1maneuver it would be at the aft end of the M-2engine system, 420 feet from the ship’s nose, and atthe start of the M-2 maneuver it would be at thefront of the M-2 system, 265 feet from the nose. Asthe ship grew progressively shorter, the spin radiuswould decrease, forcing faster rotation to maintainthe same artificial gravity level. The report proposedjoining the aft end of the crew vehicle to the end of aservice vehicle during return to Earth, after the M-3engine system was cast off, in order to place the cen-ter of rotation at the joint between the two vehiclesand permit an acceptable rotation rate.

The General Dynamics crew ship design included theLife Support Section (LSS) for the eight-person crew.The LSS, which would be tested attached to an Earth-orbital space station beginning in November 1968,again illustrated the intense modularity of the

General Dynamics design. The 10-foot-diameter cen-tral section would be attached to the front of the spinemodule and would house the repair shop, food storage,and radiation-shielded Command Module (not to beconfused with the Apollo CM). The Command Modulewould serve double duty as the ship’s radiation shelterand “last redoubt” if all other habitable modules weredestroyed. Crewmembers would sleep in theCommand Module’s lower level to reduce their overallradiation exposure. The top level would serve as thecrew ship’s bridge and the “blockhouse” from which theservice vehicles would be remote-controlled.

Two-level, 10-foot-diameter Mission Modules wouldcluster around the central section to provide additionalliving space. Individual levels could be sealed off if pen-etrated by meteoroids, and entire Mission Modulescould be cast off if the crew had to reduce spacecraftmass to permit return to Earth—for example, if a largeamount of propellant were lost and could not bereplaced from the service vehicles. The LSS would alsoinclude the Earth Entry Module, an Apollo CM-styleconical capsule. In addition to carrying the astronautsthrough Earth’s atmosphere at voyage’s end, it wouldserve as emergency abort vehicle during the M-1maneuver. The service vehicles would each carry aspare Earth Entry Module.

On the service ships, a hangar for robot probes wouldreplace the LSS. Unlike the Lockheed andAeronutronic reports, the General Dynamics reporttreated its automated Mars probes in some detail.They would include the Returner Mars sample collec-tor, a Mars Lander based on technology developed forNASA’s planned Surveyor lunar soft-landing probes,Deimos Probe (Deipro) and Phobos Probe (Phopro)Mars moon hard landers based on technology devel-oped for NASA’s Ranger lunar probes, the MarsEnvironmental Satellite (Marens) orbiter, andFloater balloons.13

General Dynamics’ EMPIRE statement of workspecified that it should study piloted Mars-orbitalmissions; however, enthusiastic Ehricke could notresist inserting an option to carry a small pilotedMars lander. A piloted Mars orbiter must, after all,enter and depart Mars orbit, thus performing all themajor maneuvers required of a Mars OrbitRendezvous landing mission except the landing itself.The Mars Excursion Vehicle lander, which would be



based on the automated Returner, would be carried ina service vehicle probe hangar. It would support twopeople for seven days on Mars.14 Ehricke’s team pro-posed that a crew test it on the Moon in November1972.

To get its ships into Earth orbit, Ehricke’s teaminvoked a very large post-Saturn heavy-lift rocketcapable of launching 500 tons. Two of these giantswould be able to place parts for one ship into orbit so thatonly one rendezvous and docking would be required tocomplete assembly. By contrast, if the Saturn C-5 wereused, eight launches and seven rendezvous and dockingmaneuvers would be needed to launch and assembleeach General Dynamics Mars ship. The Ehricke teamtargeted post-Saturn vehicle development to commencein July 1965; the giant rocket would be declared opera-tional in August 1973.

Mars in Texas

NASA’s Manned Spacecraft Center (MSC) (renamedthe Johnson Space Center in 1973) began as the SpaceTask Group (STG) at NASA Langley Research Centerin Hampton, Virginia, where it was formed in late1958 to develop and manage Project Mercury.Following Kennedy’s May 1961 Moon speech, theSTG’s responsibilities expanded, so it needed a newhome. The STG became the MSC and moved toHouston, Texas.

Maxime Faget became MSC’s Assistant Director forResearch and Development. He launched the first MSCpiloted Mars mission study in mid-1961, but itremained in-house and at a minimal level of effort untillate 1962, after Marshall kicked off EMPIRE. MSC’sstudy was supervised by David Hammock, Chief ofMSC’s Spacecraft Technology Division, and BruceJackson, one of his branch chiefs. Chief products ofMSC’s study were a Mars mission profile unlike anyproposed up to that time and the first detailed MarsExcursion Module (MEM) piloted Mars lander design.

Jackson and Hammock presented MSC’s Mars plan atthe first NASA intercenter meeting focused on inter-planetary travel, the Manned Planetary MissionTechnology Conference held at Lewis from 21 to 23May 1963. The NASA Headquarters Office of AppliedResearch and Technology organized the meeting,

which focused mainly on specific technologies, manywith applications to missions other than Mars. The“Mission Examples” session, chaired by Harry Ruppe,was relegated to the afternoon session on the last dayof the meeting.

Hammock and Jackson presented MSC’s missiondesign publicly for the first time at the AmericanAstronautical Society (AAS) Symposium on theManned Exploration of Mars in Denver, Colorado, thefirst non-NASA conference devoted to piloted Marstravel.15 George Morgenthaler of Martin MariettaCorporation in Denver organized the symposium. Asmany as 800 engineers and scientists heard 26 papersand a banquet address by Secretary of the Air ForceEugene Zuckert. It was the first time so many individ-uals from Mars-related disciplines came together inone place, and the last Mars conference as large untilthe 1980s. Sky & Telescope magazine reported that the“Denver symposium . . . helped narrow the gapsbetween engineer, biologist, and astronomer.”16

Hammock and Jackson called Mars “perhaps themost exciting target for space exploration followingApollo . . . because of the possibility of life on its sur-face and the ease with which men might be sup-ported there.”17 Two of their plans used variations onthe MOR mode, but the third, dubbed the Flyby-Rendezvous mode, was novel—it would accomplish apiloted Mars landing while still accruing theweight-minimization benefits of a Crocco-type flyby.

The Flyby-Rendezvous mode would use two separatespacecraft, designated Direct and Flyby. They wouldreach Earth orbit atop Saturn V rockets. The unpilotedFlyby craft would depart Earth orbit 50 to 100 daysahead of the piloted Direct craft on a 200-day trip toMars. The Direct craft, which would include the MEMlander, would reach Mars ahead of the Flyby craft aftera 120-day flight. The astronauts would then board theMEM and abandon the Direct craft. The MEM wouldland while the Direct craft flew past Mars into solarorbit. Forty days later the Flyby craft would pass Marsand begin the voyage back to Earth. The crew would liftoff in the MEM ascent vehicle and set out in pursuit,boarding the Flyby craft about two days after leavingMars. Near Earth the astronauts would separate fromthe Flyby spacecraft in an Earth-return capsule, enterEarth’s atmosphere, and land.



One of MSC’s MOR plans used aerobraking, while theother relied on propulsive braking. In aerobraking, thelifting-body-shaped Mars spacecraft would skimthrough Mars’ upper atmosphere to use drag to slowdown and enter orbit. The Mars surface explorerswould separate from the orbiting ship in the MEM andland for a surface stay of 10 to 40 days. They wouldthen lift off in the MEM ascent stage, dock with theorbiting ship, and leave Mars orbit. Earth atmospherereentry would occur as in the Flyby-Rendezvous mode.Hammock and Jackson’s propulsive-braking MORmission resembled the aerodynamic-braking modedesign, except that a chemical or nuclear propulsionstage would place the ship in Mars orbit.

Hammock and Jackson found that the chemical all-propulsive spacecraft design would weigh the mostat Earth-orbit departure (1,250 tons), while thenuclear aerobraking design would weigh the least

(300 tons). The Flyby-Rendezvous chemical and aer-obraking chemical designs would weigh about thesame (1,000 tons).

The MEM design for the Houston Center’s MORplans—the first detailed design for a piloted Marslander—was presented in June 1964 at the nextmajor meeting devoted to Mars exploration, theSymposium on Manned Planetary Missions atMarshall.18 Philco (formerly Ford) Aeronutronic per-formed the study between May and December 1963.Franklin Dixon, the presenter, was Aeronutronic’smanager for Advanced Space Systems. The design,which the company believed could land on Mars in1975, was first described publicly in Houston inNovember 1964 at the American Institute ofAstronautics and Aeronautics (AIAA) 3rd MannedSpace Flight Conference.



Figure 1—Landing on Mars. Aeronutronic’s Mars lander, a lifting body glider, relied on aerodynamic lift to minimize requiredpropellant. The design was based on optimistic estimates of Martian atmospheric density. (“Summary Presentation: Study ofa Manned Mars Excursion Module,” Franklin Dixon, Proceeding of the Symposium on Manned Planetary Missions:1963/1964 Status, NASA TM X-53049, Future Projects Office, NASA George C. Marshall Spaceflight Center, Huntsville,Alabama, June 12, 1964, p. 467.)

Dixon pointed out that the chief problem facing Marslander designers was the lack of reliable Mars atmos-phere data, noting that “two orders of magnitude vari-ations in density at a given altitude were possiblewhen comparing Mars atmosphere models of respon-sible investigators.” Aeronutronic settled on aMartian atmosphere comprising 94 percent nitrogen,2 percent carbon dioxide, 4 percent argon, and tracesof oxygen and water vapor, with a surface pressure of85 millibars (about 10 percent of Earth sea-level pres-sure). For operation in this atmosphere, Aeronutronicproposed a “modified half-cone” lifting body with twostubby winglets. The Aeronutronic MEM would meas-ure about 30 feet long and 33 feet wide across its tail.The 30-ton MEM would ride to Mars on its mother-ship’s back under a thermal/meteoroid shield whichthe crew would eject two hours before the Marslanding. The three-person landing party, whichwould consist of the captain/scientific aide, first offi-cer/geologist, and second officer/biologist, would donspace suits and enter the small flight cabin in theMEM’s nose. Five minutes before planned deorbit,the MEM would separate from its mothership andretreat to a distance of 1,000 feet. There it wouldpoint its tail forward and fire its single descentengine to begin the fall toward Mars’ surface.

The MEM’s heat-resistant hull would be madelargely from columbium, with nickel-alloy aft sur-faces. Aeronutronic calculated that friction heatingwould drive nose temperature to 3,050 degreesFahrenheit. At Mach 1.5, between 75,000 and100,000 feet above Mars, a single parachute wouldbe deployed and the MEM would assume a tail-downattitude. The engine would then ignite a second timeand the parachute would separate. Aeronutronic’sdesign included enough propellant for an estimated60 seconds of hover before touchdown on four land-ing legs with crushable pads.

Aeronutronic attempted to select a MEM landing siteusing photographs taken by Earth-based telescopes.Theorizing that living things might follow the retreat-ing edge of the melting polar cap in springtime, theysuggested that NASA target the MEM to Cecropia at65 degrees north latitude (this corresponds to VastitasBorealis north of Antoniadi crater on modern Marsmaps).19 Upon landing, the astronauts would ejectshields covering the MEM windows and look out over

their landing site to evaluate “local hazards,” includingany “unfriendly life forms.”20 Mars surface access wouldbe through a cylindrical airlock that lowered like anelevator from the MEM’s tail.

Dixon stated that “biological evaluation of life forms isessential for the first purely scientific effort to allowpre-contamination studies before man alters the Marsenvironment,”21 implying that little effort would bemade to prevent the astronauts from introducing ter-restrial microorganisms. Aeronutronic listed “investi-gate life forms for possible nutritional value”22 amongthe tasks of the Mars biology study program. The crewwould explore Mars for between 10 and 40 days, spend-ing about 16 man-hours outside the MEM each day.

Aeronutronic’s MEM was envisioned as a two-stagevehicle. For return to Mars orbit, the ascent motorwould fire, blasting the flight cabin free of the descentstage. Two propellant tanks would be cast off duringascent. After docking with the orbiting mothership, theMEM flight cabin would be discarded.



Figure 2—Astronauts exploring Mars near Aeronutronic’slander would take pains to collect biological specimens beforeterrestrial contamination made study impossible. A largedish antenna (left) would let them share their discoverieswith Earth. (“Summary Presentation: Study of a MannedMars Excursion Module,” Franklin Dixon, Proceeding of theSymposium on Manned Planetary Missions: 1963/1964Status, NASA TM X-53049, Future Projects Office, NASAGeorge C. Marshall Spaceflight Center, Huntsville,Alabama, June 12, 1964, p. 470.)

UMPIRE

Every 26 months, an opportunity occurs for a short (six-month) minimum-energy transfer from Earth to Mars.In some opportunities the planet is farther from Earththan in others. This means that in some opportunitiesthe minimum energy necessary to reach Mars isgreater than in others. The most difficult Mars oppor-tunities require about 60 percent more energy than thebest opportunities. The more energy required to reachMars, the more propellant a spacecraft must expend.Because of this, a spacecraft launched in a poor Marsopportunity will weigh more than twice as much as onelaunched in a good Mars opportunity.

The quality of Mars launch opportunities runsthrough a continuous cycle lasting about 15 years. Notsurprisingly, this corresponds to the cycle of astronom-ically favorable oppositions described in Chapter 1.The EMPIRE studies showed that the best Mars

opportunities since 1956 would occur in 1969 and1971, just as the Apollo lunar goal was reached.Opportunities would become steadily worse after that,hitting a peak in 1975 and 1977, then would gradual-ly improve. The next set of favorable oppositions wouldoccur in 1984, 1986, and 1988.

The Marshall Future Projects Office contracted withGeneral Dynamics/Fort Worth and Douglas AircraftCompany in June 1963 to “survey all the attractivemission profiles for manned Mars missions during the1975-1985 time period, and to select the mission pro-files of primary interest.” The study, nicknamed“UMPIRE” (“U” stood for “unfavorable”), was summedup in a Future Projects Office internal report inSeptember 1964.23

General Dynamics and Douglas worked independently,but each found that the “best method of alleviating thecyclic variation of weight required in Earth orbit is to



Figure 3—Returning to Mars orbit: Like the Apollo Lunar Module, Aeronutronic’s lander design used its descent stage as alaunch pad for its ascent stage. Unlike the Lunar Module, it cast off spent propellant tanks as it climbed to orbit. (“SummaryPresentation: Study of a Manned Mars Excursion Module,” Franklin Dixon, Proceeding of the Symposium on MannedPlanetary Missions: 1963/1964 Status, NASA TM X-53049, Future Projects Office, NASA George C. Marshall SpaceflightCenter, Huntsville, Alabama, June 12, 1964, p. 468.)

plan long (900-1100 days) missions.”24 The companiesadvised that “serious consideration . . . be given to theconcept of the first manned landing on Mars being along term base” rather than a short visit.25 That is, thetwo companies recommended making the first Marsexpedition conjunction class, not opposition class.

The terms “conjunction class” and “opposition class”refer to the position of Mars relative to Earth duringthe Mars expedition. In the former, Mars moves behindthe Sun as seen from Earth (that is, it reaches conjunc-tion) halfway through the expedition; in the latter,Mars is opposite the Sun in Earth’s skies (that is, atopposition) at the expedition’s halfway point.

Conjunction-class expeditions are typified by low-energy transfers to and from Mars, each lasting aboutsix months, and by long stays at Mars—roughly 500days. Total expedition duration thus totals about1,000 days. The long stay gives Mars and Earth timeto reach relative positions that make a minimum-energy transfer from Mars to Earth possible. VonBraun opted for a conjunction-class expedition in TheMars Project.

Opposition-class Mars expeditions have one low-energytransfer and one high-energy transfer separated by ashort stay at Mars—typically less than 30 days. Totalduration is about 600 days. This was the approach

Lewis used in its 1959-1961 study. In the 1960s, mostMars expedition plans were opposition class.

Because they require more energy, opposition-classexpeditions demand more propellant. All else beingequal, a purely propulsive opposition-class Mars expe-dition can need more than 10 times as much propellantas a purely propulsive conjunction-class expedition.This adds up, of course, to a correspondingly greaterspacecraft weight at Earth-orbit departure.

Therefore, the conjunction-class plan is attractive.However, the long mission duration is problematical,for it demands great endurance and reliability fromboth machines and astronauts, exposes any crew left inMars orbit to risk from meteoroids and radiation for alonger period, and requires complex Mars surface andorbital science programs to enable productive use of the500-day Mars stay.

Mars in California

NASA’s Ames Research Center, a former NACA labora-tory in Mountainview, California, also became involvedin piloted Mars planning in the EMPIRE era. In 1963,Ames contracted with the TRW Space TechnologyLaboratory to perform a non-nuclear Mars landing expe-dition study emphasizing weight reduction. Robert Sohn



Figure 4—Conjunction-class Mars missions include alow-energy transfer from Earth to Mars, a long stay atMars, and a low-energy transfer from Mars to Earth. 1 -Earth departure. 2- Mars arrival. 3 - Mars departure. 4 -Earth arrival. (Manned Exploration Requirements andConsiderations, Advanced Studies Office, Engineering andDevelopment Directorate, NASA Manned Spacecraft Center,Houston, Texas, February 1971, p. 1-7.)

Figure 5—Opposition-class Mars missions offer a short Marsstay but require one high-energy transfer, so they demand morepropellant than conjunction-class missions. 1 - Earth depar-ture (low-energy transfer). 2 - Mars arrival. 3 - Mars departure(high-energy transfer). 4 - Earth arrival. (Manned ExplorationRequirements and Considerations, Advanced Studies Office,Engineering and Development Directorate, NASA MannedSpacecraft Center, Houston, Texas, February 1971, p. 1-8.)

supervised the study for TRW and presented the study’sresults at the 1964 Huntsville meeting.26 Sohn’s teamtargeted 1975 for the first piloted Mars landing.

TRW found that the biggest potential weight-saver wasaerobraking. For its aerobraking calculations, it usedthe Rand Corporation’s August 1962 “ConjecturalModel III Mars Atmosphere” model, which posited aMartian atmosphere consisting of 98.1 percent nitro-gen and 1.9 percent carbon dioxide at 10 percent ofEarth sea-level pressure. This atmospheric density andcomposition dictated the spacecraft’s proposed shape—a conical nose with dome-shaped tip, cylindrical centersection, and skirt-shaped aft section. This shape wasbased on an Atlas missile nose cone. The TRW team’stwo-stage, 12.5-ton MEM would also use the nose-coneshape. All else being equal, a version of TRW’s space-craft for the 1975 Mars launch opportunity that usedbraking rockets at Mars and Earth would weigh 3,575tons, while the company’s aerobraking design wouldweigh only 715 tons.

TRW’s Earth aerobraking system was the EarthReturn Module, a slender half-cone lifting body carriedinside the main spacecraft. A few days before Earthencounter the crew would enter the Earth ReturnModule and separate from the main spacecraft. TheEarth Return Module would enter Earth’s atmosphereas the main spacecraft flew past Earth into solar orbit.

The TRW study proposed a lightweight artificial grav-ity system—a 500-foot tether linking the main space-craft to the expended booster stage that pushed it fromEarth orbit—which would, it calculated, add less than1 percent to overall spacecraft weight. The resultantassemblage would spin end over end to produce artifi-cial gravity. TRW reported that NASA Langley hadused computer modeling to confirm this design’s long-term rotational stability.27

TRW found that Earth-Mars trajectories designed toreduce spacecraft weight at Earth departure wouldresult in high reentry speeds at Earth return. Forexample, an Earth Return Module would reenter at66,500 feet per second at the end of a 1975 Mars voy-age, while one returning after a 1980 mission wouldreenter at almost 70,000 feet per second. TRW foundthat available models for predicting atmospheric fric-tion temperatures broke down at such speeds.28 Forcomparison, maximum Apollo lunar-return speed was“only” 35,000 feet per second.

Reentry speed could be reduced by using rockets. TRWfound, however, that including enough propellant toslow the entire spacecraft from 66,500 feet per secondto 60,000 feet per second would boost spacecraft weightfrom 715 tons to 885 tons. Slowing only the EarthReturn Module by the same amount would increaseoverall spacecraft weight to 805 tons.

The study proposed a new alternative—a Venus swing-by at the cost of a modest increase in trip time. A shipreturning from Mars in 1975 could, the study found, cutits Earth reentry speed to 46,000 feet per second bypassing 3,300 kilometers over Venus’s night side. AVenus swingby during flight to Mars in 1973 wouldallow the ship to gain speed without using propellantand thus arrive at Mars in time to take advantage of aslower Mars-Earth return trajectory. According toTRW’s calculations, Venus swingby opportunitiesoccurred at every Mars launch opportunity.29



Figure 6—TRW’s 1964 Mars ship design, shaped like amissile warhead, sought to minimize required propellantby aerobraking in the Martian atmosphere. This cutawayshows the Mars lander and Earth Return Module insidethe spacecraft. (“Summary of Manned Mars MissionStudy,” Robert Sohn, Proceeding of the Symposium onManned Planetary Missions: 1963/1964 Status, NASATM X-53049, Future Projects Office, NASA George C.Marshall Spaceflight Center, Huntsville, Alabama, June12, 1964, p. 150.)

Building on Apollo

By the end of the June 1964 Marshall Mars sympo-sium, early flyby detractor Maxime Faget had cometo see some merit in the concept. In a panel discus-sion chaired by Heinz Koelle, Faget declared that“we should, I think, consider a flyby . . . if we under-take a flyby we really have to face the problems ofman flying out to interplanetary distances . . . . Ithink we have to undertake a program that will forcethe technology, otherwise we will not get [to Mars] inmy lifetime . . . .”30

Von Braun, also a panel member, added, that “I think[piloted] flyby missions, particularly flybys involving[automated] landing probes . . . would be invaluable. . . . One such flight, giving us more information onwhat to expect . . . on the surface of Mars, will beextremely valuable in helping us in laying out theequipment for the landing . . . that would follow thefirst flyby flight.” 31

Von Braun then implicitly announced an impendingshift in NASA advanced planning. “I am also inclined tobelieve,” he said, “that our first manned planetary flybymissions should be based on the Saturn V as the basicEarth-to-orbit carrier. The reason is that, once the pro-duction of this vehicle is established and a certain reli-ability record has been built up, this will be a vehiclethat will be rather easy to get.” Von Braun’s statementacknowledged that a post-Saturn rocket appearedincreasingly unlikely.32 In an outline of future planssubmitted to President Lyndon Johnson’s BudgetBureau in late November 1964, NASA stated that thepost-Saturn rocket should receive low funding priority,and called for post-Apollo piloted spaceflight to befocused on Earth-orbital operations using technologydeveloped for the Apollo lunar landing.33

The 1964 decision to use Apollo technology for missionsafter the lunar landing could be seen as a rejection ofpost-Apollo piloted Mars missions. Historian EdwardEzell wrote in 1979 that the “determinism to utilizeApollo equipment for the near future was very destruc-tive to the dreams of those who wanted to send men toMars.”34 As if to emphasize this, the amount of fundingapplied to piloted planetary mission studies took a nosedive after November 1964. In the 17 months precedingNovember 1964, $3.5 million was spent on 29 pilotedplanetary mission studies. Between November 1964

and May 1966, NASA contracted for only four suchstudies at a cost of $465,000.35

Mars planners were not so easily discouraged, however.After EMPIRE, and concurrent with UMPIRE, aMarshall Future Projects Office team led by Ruppe com-menced an in-house study to look at using Apollo hard-ware for Mars exploration. Ruppe’s study report, pub-lished in February 1965, found that piloted Mars flybymissions would be technically feasible in the mid- to late-1970s using Saturn rockets and other Apollo hardware. 36

The report’s flyby spacecraft design used hardwarealready available or in an advanced state of development.Two RL-10 engines would provide rendezvous and dock-ing propulsion, for example, and an Apollo Lunar Moduledescent engine would perform course corrections.

A pressurized hangar would protect a modified ApolloCSM during the interplanetary voyage. The hangarwould also provide a shirt-sleeve environment so thatthe astronauts could act as in-flight caretakers forfive tons of automated probes, including “landers,atmospheric floaters, skippers, orbiters, and possiblyprobes . . . to perform aerodynamic entry tests [of]designs and materials.”37 The last of these would,Ruppe wrote, provide data to help engineers designthe piloted Mars landers to follow. His report drew onthe UMPIRE conclusions when it stated that

significant reduction of initial mass in Earthorbit is possible if we can use aerodynamicbraking at Mars or refueling there, but thesemethods assume a knowledge about . . . theMartian atmosphere, or about Mars surfaceresources which just is not available. The firstventure, still assuming that we are not veryknowledgeable . . . would probably transport 2or 3 men to the surface of Mars for a few days. . . [at a cost of] a billion dollars per man-dayon Mars. If the physical properties of Marswere well known, we could think . . . of the firstlanding as a long-duration base, reducing costto less than 10 million dollars per man-day.38

The three-person flyby crew would live in a sphericalhabitat containing a radiation shelter and a small cen-trifuge for maintaining crew health (the study rejectedartificial gravity systems that rotated the entire craft asbeing too complex and heavy). Twin radioisotope powerunits on extendible booms would provide electricity.



The mission would require six Saturn V launches andone Saturn IB launch. Saturn V rocket 1 would launchthe unpiloted flyby spacecraft; then Saturn V rockets 2through 5 would launch liquid oxygen tankers. Thesixth Saturn V would then launch the Earth-departurebooster, a modified Saturn V second stage called the S-IIB, which would reach orbit with a full load of 80 tonsof liquid hydrogen but with an empty liquid oxygentank. Ruppe wrote that solar heating would cause theliquid hydrogen to turn to gas and escape; to ensurethat enough remained to boost the flyby craft towardMars, the S-IIB would have to be used within 72 hoursof launch from Earth.

The three astronauts would launch in the modifiedApollo CSM on the Saturn IB rocket and then boardthe flyby spacecraft. They would use the RL-10engines to guide the flyby craft to a docking with theS-IIB. The oxygen tankers would then dock in turn andpump their cargoes into the S-IIB’s empty oxygentank. Ruppe’s flyby craft and booster would weigh 115tons at Earth-orbit departure. The S-IIB would thenignite, burn to depletion, and detach, placing the flybycraft on course for Mars.

During the flight, the astronauts would regularlyinspect and service the automated probes. As theyapproached Mars, the astronauts would release theprobes and observe the planet using 1,000 pounds ofscientific equipment. The flyby spacecraft would relayradio signals at a high data rate between the Marsprobes and Earth until it passed out of range; thendirect communication between Earth and the probeswould commence at a reduced data rate.

As Earth grew large again outside the viewports, theflyby astronauts would enter the modified Apollo CSMand abandon the flyby craft. The CSM’s propulsion

system would slow it to Apollo lunar return speed,then the CM would separate from the SM, reenter, andland. Depending on the launch opportunity used, totalmission duration would range from 661 to 691 days.

Even as Ruppe’s report was published, the “robot care-taker” justification for piloted Mars flybys was becom-ing increasingly untenable. On 31 July 1964, theRanger 7 Moon probe snapped 4,316 images of one cor-ner of Mare Nubium before smashing into the lunarsurface as planned. The images showed the Moon to besufficiently smooth for Apollo landings, and gave thecredibility of robot explorers a vital boost. As Ruppepublished his report, Mariner 4, launched on 28November 1964, was making its way toward Mars. Notlong after Ruppe published his report, on 20 February1965, Ranger 8 returned 7,137 images as it plungedtoward the Sea of Tranquillity. A month later, Ranger 9returned 5,148 breathtaking images of the complex112-kilometer crater Alphonsus.

Beyond providing engineering and scientific justifica-tions for the piloted flyby mission, Ruppe’s report ten-dered a political justification. He wrote:

From the lunar landing in this decade to apossible planetary landing in the early ormiddle 1980s is 10 to 15 years. Without amajor new undertaking, public support willdecline. But by planning a manned planetary[flyby] mission in this period . . . the UnitedStates will stay in the game.39

That Ruppe felt it necessary in early 1965 to attempt tojustify a piloted Mars flyby mission in terms of proba-ble impact on the U.S. domestic political environment istelling, as will be seen in the next chapter.



Documents

Chapter 3: EMPIRE and After - NASA 3.pdf · They assumed a Nova rocket capable of lifting 250 tons to Earth orbit. For comparison, the largest planned Saturn rocket, the Saturn C-5